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1. INPUT&OUTPUTDEVICES
Input devices:
Inputdevices the inputunitisresponsibleforacceptinginputi.e.data&instructionsfromthe user.The
workis accomplishedwiththe helpof inputdevices like:-
OUTPUT DEVICES:
OUTPUT DEVICESThe output unit isresponsible forproducingthe outputinuserreadable form.Various
outputdeviceslike monitor(alsocalledVDUi.e.visual displayunit), printer,plotteretc.makesthe
outputunitof computer.
 Monitors:
 Monitoror screenisthe mostcommon formof outputfrom a computer. It displaysinformation
ina similarwaytothat shownon a televisionscreen.The picture onthe monitorismade upof
thousandsof tinycoloreddotscalledpixels.CATHODERAY TUBE (CRT):- itworksinthe same
wayas a television –itcontainsan electrongunat the back of the glass tube whichfires
electronstomake the screenglow.LIQUIDCRYSTAL DISPLAY(LCD):- liquidcrystal isthe material
usedto create eachpixel onthe screen.Each tinycell of liquidisapixel.
 Printers:
 Printers a mostconvenientandusefulmethodbywhichthe computercandeliverinformationis
by meansof printedcharacters.Printerscanbe dividedintwodistinctcategories.Impact
printers:Inthisprinters,there ismechanical contactbetweenthe printerheadandpaper. Non-
impactprinters:Inthisprinters,there isnomechanical contactbetweenthe printerheadand
paper.
1. Impact printers:
Impact printer’s Dotmatrix printer:A dotmatrix printer(DMP) is the mostpopularserial printer
i.e.itpointsone characterat a time.InDMPS, the printingheadcontainsa vertical arrayof pins.
As the headmovesacrossthe paper,selectedpinsfire againstaninkribbontoforma patternof
dotson the paper.There are 80 columnsDMPs and 132 columnsDMPs available ionthe market.
2. Non-impact printers:
Non-impactprinters’ 1.Electromagneticprinters:Byusingmagneticrecordingtechniques,a
magneticimage whatisto be printedcan be writtenonas drum surface. 2. Thermal printers:An
electricpulse can

2. Be convertedtoheaton selectedsectionsof aprintingheadoron wiresornibs.Whenthisheat
isappliedtoheatsensitive paper,acharacter isprinted.
3. Electrostatic printers: Forelectrostaticprintersthe paperiscoatedwitha non
conductingdielectricmaterial whichholdchargeswhenvoltagesare appliedwithwriting
“nibs”(heads).Thisheadswrite dotsonpaperas itpasses.
4. Inkjet printer: Printersdirectahigh-velocitystreamof inktowardthe paper.The ink
streamis brokenintodropletsbyanultrasonictransducers.
5. Laser printer: Thisprintersmake use of office copiertechnologies.The desiredoutput
image iswrittenona copierdrum withthe helpof a lightbeamcontrolledbyacomputer.
These laserprintersare quite andare capable of producingveryhighpointquality.The speed
of laserprinterscanbe upto10-15 pagesperminute (ppm).
 Speakers:
 Speakers:Speakersreceivesthe soundsinformof electriccurrentfromthe soundcard andthen
convertit to soundformat.
 RANDOM ACCESS MEMORY (RAM):
 RANDOMACCESS MEMORY (RAM) in the ram the memorycellscanbe accessedforinformation
transferfromany desiredrandomlocationi.e.the processof locatingawordin memoryisthe
same and requiresanequal amt.of memory,thus the name “random access”.
 DRAM (DYNAMIC RAM):
 DRAM(DYNAMICRAM) it consistsof a transistorand capacitorthat’scapable of storingan
electriccharge. Dependingonthe switchingactionof the transistorthe capacitoreithercontains
no charge (0) or doesholda charge (1).DRAMSTORAGE Density since aDRAM cell consistsof
one transistorand capacitorper bit,itallowsa DRAMchipto pack a large numberof cellswithin
the chip comparedtoSRAM. GenerallyaDRAMchipsare available with128 bitor 256 bits
densitiesorevenmore.DRAMrefreshing the problemof acapacitor istheyit starts loosingthe
charge overa periodof time,&can retaindatafor barelya thousandthof a second.So,the
memorycontrollerneedstorefreshthe memorycontentsasmanyas thousandtimesasecond,
whichiscalledmemoryrefreshing.
 Types of DRAM:
 Typesof DRAM EDO DRAM: An EDO RAMcell keepsitsdatavaliduntil itreceives anadditional
signal.Ithas a duel-pipeline architecture,whichallowsthe memorycontrollersimultaneously
readnewdata while discharge the old.SynchronousDRAM(SDRAM):Withthe arrival of higher
speedprocessors, Designers of systemsoonfeltthe needtorunmemorybusfasterthan66
MHz thiswasmade possiblebyredesigningthe basicmemorychipinterface.These improved
memorychipswere calledSDRAM.Rambusdram(RDRAM):the Rambusprotocol createsan
independentcontrol andaddressbusanddata istransmittedacrossa16 bitwide databus.
Double datarate (DDR) SDRAM: Unlike SDRAMmemorythe supportone operationineach
clock,DDR SDRAMmemorycando two operationperclock,there bydouble memorybandwidth
oversingle datarate SDRAM.

3. 1. Static RAM:
StaticRAM consistseventuallyof internal flip-flopsthatstore the binaryinformation.The stored
informationremainsvalidaslongaspowerisappliedtothe unit.ReadOnlyMemory(ROM):-
ReadOnlyMemory(ROM) isa memoryunitthatperformsthe readoperationonly;itdoesnot
have a write capability.Thisimpliesthatthe binaryinformationstoredROMismade permanent
duringthe hardware productionof the unitand cannotbe alteredbywritingdifferentwords
intoit (non-volatile).A ROMis restrictedtoreadingwordsthatare permanentlystoredwithin
the unit.Programmable ReadOnlyMemory(PROM) isa ROMthat can be programmedto
record informationusingafacilityknownasPROM- Programmer.Once the Chiphasbeen
programmed,the recordedinformationcannotbe changedi.e.prombecomessame asROM.
Erasable Programmable ReadOnlyMemory(EPROM) isanothertype of ROMthat can be erased
and chopcan be re programmedtorecord differentinformationusingaspecial PROM- program
me facility.Electricallyerasable PROM(EEPROM) of ROM can be programmedanderasable by
electricsignal.Itdoesnotrequire expose toultravioletlighterase itscontentsasEROMmemory
does,andprovidesaneasymeansto loadthe storedtemporaryor permanentinformationin a
formof ROMmemory.
2. Cache Memory:
Cache Memory the Cache Memory isa highspeedmemoryavailableinside CPUinorderto
speedupaccessto data and instructionsstoredinRAMmemory.A memorycache,some times
calledcache store or RAM cache, is a portionof memorymade of highspeedstaticRAM(SRAM)
insteadof the slowerandcheaperdynamic RAM(DRAM) usedformemorymainmemory.
Memorycaching iseffective because mostprogramsaccessthe same data or instructionsover
and over.By keepingasmuchof thisinformationaspossibleinSRAM,the computeravoids
accessingthe slowerDRAM.
 The Secondary MemoryDevice:
The SecondaryMemoryDevice Since primarymemoryhasa limitedstorage capacityandisnot
permanent,secondarystorage devicesare vused tostore large amountof data permanently.The
followingsecondarydevicesavailable these days.
(i) MagneticMedia:-Harddisks,FloppyDisks.
(ii) Optical Media:- CD ROMs, DVDs.kilobytes(KBs),megabytes (MBs), gagabytes(GBs),and
tera bytes(TBs) aswe dofor mainmemory.
1. Floppy Disks:
FloppyDisksThe floppydisksare one of the portable storage device still inuse.The floppydisks
enable one totransfersmall filesbetweencomputersandalsotostore data/informationas
back up.The floppydisk ismade of a flexible substancescalledMylar.Theyhave amagnetic
surface whichallowsthe recordingof data. A standardfloppydiskcanstore up to 1.44MB of
data equivalentto300A4 size paper.Howevergraphics/picturecan store init as
graphics/picture.

4. 2. Hard Disks:
Hard Disks the hard diskmemoriesstore informationonone ormore circularsplatters(or
disks) whichare continuallyspinning.Thisrotationdisksare coatedwithmagneticmaterial
and stackedwithspacesbetweenthem.Informationisrecordedonthe surface of the rotating
disks.Bymagnetictapesas tinymagneticspots.These headsare mountedonaccessarms.
Informationisrecordedinbands.Eachband of informationona givendiskiscalledatrack.
Storage capacityof hard diskismeasuredbygigabytesintoday,mostcommonbeing80 GB to
300 GB.
3. Compact Disks (CD):
CompactDisks(CD) The CDs are optical media. The CDsare relativelychip&have a storage
capacityof up to 700 Mb. There are 3 maintypesof CDs. CD-ROM(CompactDisk-readOnly
Memory):Thisisusedonlyto store information&cannotbe usedforstore data. CDROM
comeswitha reportedspeedof 48x to 75x. CD-R(CompactDisk-recordable):Datacanbe
recordedonthose diskonlyonce on one part of the diskandanother part at latertime
onetime each.Thisdiskcannotbe erased.CD-RW(CompactDisk- Rewritable):CD-RWisan
erasable disk,one canwrite multiple times.Itovercomesthe difficultyof writingonce on
CDs.CD-RWdisksare more like floppy/harddisksasdataare erasable and rewritable.
4. DVDs:
DVDsDVD is an optical storage device thatlooksthe same asa CD butstorage capacity 15
timesmore thanCD and transferdata to computer20 timesfasterthanCD-ROM.DVDs also
come in three verities.DVD-ROMDigital VideoDisk –ReadOnly Memory. DVD-ROMishigh
capacityoptical diskcapable of storing4.7 GB to 17 GB. Huge capacity makesthemattractive
for storinglarge amountsof data. DVD-R(DVD-Recordable).DVD-RsimilartoCD-R’sallow
usersto write once andin multiple timesbutreaditmanytimes.DVD-RW(DVD-Rewritable).
Most rewritable DVDdrivesare DVD-RW.One canerase and readmany timesonthem.
Because of there enormouscapacitytheyare replacingCDtechnology.
CD/DVDDRIVE:
5. Pen/Thumb Drives – FlashMemories:
Pen/ThumbDrives –FlashMemories anotherkindof storage device hasrecentlyemerged.It
iscalledFlash memory, USBmemory,the thumbdrives/pendrivesandcell phonestodayuse
flashmemories.Flushisa‘solidstate’memoryi.e.ithasnomovingpartsunlike magnetic
storage devices.Nordoesitmake USE of lasers- unlikeoptical drives.Dataisretainedinflash
memoryevenwhenpowerisswitchedoff.